Turkish police on Thursday have detained 11 ISIS-linked suspects in helicopter-backed dawn raids carried out in Istanbul.The raids were part of a series of operations against suspected militants in Turkey, where security is being tightened ahead of the G20 world leaders' summit being staged this weekend.Last week, police detained 20 people suspected of links to ISIS in the southern resort province of Antalya, where the G20 summit is being held from Nov. 15-16.The anti-terror squad police carried out simultaneous raids on more than 20 addresses in various districts of Istanbul, with seven foreigners among those held, Anadolu said.It said the operation was continuing and more people might be detained.Ankara has been doing its part to identify and stop potential foreign fighters seeking to cross the border to Syria to join ISIS despite little cooperation in intelligence sharing with its Western allies. As part of efforts, the police force has tightened security at transfer points such as airports, terminals, bus stations and rental car companies. The police have done so by employing a special risk analysis system and a team tasked with tracking suspicious foreigners who travel to Turkey for the first time and minors who have made no hotel reservations.